What it means
Not all bank capital is equally useful in a crisis. Common Equity Tier 1 is the purest form because it is permanent, carries no obligation to repay and absorbs losses immediately as they arise, unlike debt instruments that only convert or write down when specified triggers are hit.
Certain items are deducted from it, notably goodwill, other intangible assets and some deferred tax assets, because they would not realise value in a stress. The CET1 ratio matters because it drives what a bank can do.
Fall below the combined requirement and automatic restrictions kick in on dividends, share buybacks and bonuses, so a board watching the ratio drift down will cut distributions long before a regulator has to say anything. Analysts and rating agencies read the ratio as the primary measure of a bank's ability to survive a downturn.
The denominator is as important as the numerator. Risk-weighted assets are not simply total assets: each exposure is scaled by how risky it is judged to be, so cash and government bonds may carry a zero weighting while an unsecured corporate loan carries a full one and some exposures carry more.
This means a bank can improve its ratio either by raising capital or by shifting its lending towards lower-weighted assets. The usual nuance is the difference between the headline minimum and the actual requirement a bank faces.
The baseline minimum is 4.5%, but capital conservation buffers, countercyclical buffers, systemic importance surcharges and bank-specific supervisory add-ons stack on top, so a large bank's real requirement is often around 10% or more. Banks therefore manage to a target well above the requirement, and the gap between the two is called the management buffer or headroom.
In practice
Real-world examples.
Example
A large bank reporting a CET1 ratio of 14.2% against a requirement of 10.5% announces a share buyback, arguing the headroom is larger than it needs to carry through a downturn.
Example
A mid-sized lender fails a regulatory stress test in which its ratio falls to 5.9% under a severe scenario. The regulator blocks its planned dividend until it either raises capital or reduces higher-weighted lending.
Example
A bank shifts part of its balance sheet from unsecured business lending into residential mortgages with lower risk weightings. Total assets barely change but risk-weighted assets fall by $4 billion, lifting the reported ratio without any new equity.
Think of it
“CET1 is the abbreviation for Common Equity Tier 1-your core capital ratio.
Formula
Calculation
CET1 ratio = CET1 capital / risk-weighted assets
A bank holds CET1 capital of $19.5 billion after deductions and reports risk-weighted assets of $150 billion. Its CET1 ratio is 19.5 / 150 = 13.0%. Its regulator sets a combined requirement of 8.0%, made up of the 4.5% minimum, a 2.5% capital conservation buffer and a 1.0% bank-specific add-on, so the bank has headroom of 13.0% - 8.0% = 5.0 percentage points, which is worth 0.05 x $150 billion = $7.5 billion of capital above the requirement. If the bank then grows its corporate loan book and risk-weighted assets rise to $160 billion with no new capital raised, the ratio falls to 19.5 / 160 = 12.19%, still comfortable but showing how lending growth alone consumes roughly 0.8 percentage points of headroom.Case study
Seen in the real world.
The following is an illustrative and fictional example. Ravensworth Bank is an invented commercial lender with CET1 capital of $19.5 billion, risk-weighted assets of $150 billion and a reported ratio of 13.0% against a combined requirement of 8.0%. Its board had grown comfortable, treating the $7.5 billion of headroom as spare capacity for acquisitions.
A supervisory stress test then modelled a sharp property downturn in which credit losses of $6 billion cut CET1 capital to $13.5 billion while risk-weighted assets rose to $165 billion as borrower credit quality deteriorated. The stressed ratio came out at 13.5 / 165 = 8.18%, barely above the requirement and far below the level at which the fictional board would have been comfortable making distributions.
Ravensworth responded by cancelling a planned buyback, retaining an extra $1.2 billion of profit and selling a portfolio of higher-weighted commercial property loans. The illustrative lesson was that headroom measured against today's balance sheet can shrink dramatically when losses hit the numerator and risk weights rise in the denominator at the same time.
Watch out
Common mistakes.
- Reading the CET1 ratio as capital divided by total assets, when the denominator is risk-weighted assets and can be far smaller than the balance sheet total.
- Comparing the reported ratio with the 4.5% headline minimum, when buffers and supervisory add-ons push the real requirement much higher.
- Assuming a rising ratio always means a stronger bank, since it can also reflect shrinking lending or a shift into lower-weighted assets rather than genuine capital growth.
Questions
People also ask.
What is included in CET1 capital?
Mainly ordinary shares and retained earnings plus certain reserves, less deductions for goodwill, other intangibles and some deferred tax assets.
How does CET1 differ from Tier 1 and total capital?
Tier 1 adds certain loss-absorbing hybrid instruments to CET1, and total capital adds subordinated debt on top of that, with each layer being less able to absorb losses while the bank is still trading.
What happens if a bank breaches its combined buffer requirement?
Automatic restrictions apply to dividends, share buybacks and variable pay, calculated through what regulators call the maximum distributable amount.
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